The present invention relates to a method of manufacturing a tubular member having integral exterior protrusions. The present invention also and more particularly relates to such a method of manufacturing a fluid conduit such as an integrated or integral manifold, for example for use in a heat exchanger, comprising a hollow body having on the exterior thereof a plurality of integral, longitudinally spaced hollow risers.
Integral manifolds, for example for heat exchangers, presently are manufactured by a number of processes. One such known process provides that hollow risers are provided by conducting a deep drawing operation on a sheet of suitable material, for example aluminum sheet material, after which the sheet is bent into the form of a tube and abutting ends of the sheet are welded together. Thus is formed a tube having extending therefrom hollow risers. An obvious disadvantage of this construction is the resultant longitudinally extending welded seam that represents the potential source of leakage under high pressure operation, for example when the welded seam is not a reliably tight and rigid joint. Furthermore, the maximum length of the risers that can be formed is limited by the thickness of the sheet material employed.
This length limitation also applies to a method of fabricating a metallic conduit having exterior surface details as disclosed in U.S. Pat. No. 5,022,135. In this known process, an extruded blank is placed in a high pressure die and is exposed to a pressurized fluid, for example oil, that causes the metal of the blank to flow into cavities of the die, thus forming the exterior surface details.
U.S. Pat. No. 4,663,812 discloses a method of manufacturing an integrated or integral mandrel from an extruded hollow shape or element provided with one or more longitudinally extending solid integral protruding neck portions. From such neck portions are formed a plurality of individual solid risers that subsequently are reshaped into hollow risers by a reverse impact extrusion process. Thereafter, apertures are formed in the wall of the hollow element to communicate the interior thereof with the hollow risers. There are disclosed two different ways of forming the solid risers from the protruding neck part. A first such process involves laterally applying a press tool provided with cylindrical voids. A second method involves the removal of excess material from the neck part by means of a special cutting tool. The first process requires a high pressure to achieve the lateral cold forming process. The second method requires the removal of a substantial amount of material of the neck part and requires a substantial cost to maintain the cutting tool. Additionally, a disadvantage common to both such methods is that a further machining step is necessary to provide a manifold having a smooth surface ensuring a sharply defined transition between the hollow risers and the hollow element.